A Quantum Chemical Explanation of the Antioxidant Activity of Flavonoids

Abstract

Flavonoids are a group of naturally occurring antioxidants, which over the past years have gained tremendous interest because of their possible therapeutic applicability. The mechanism of their antioxidant activity has been extensively studied over several decades. However, there is still much confusion about the molecular mechanism of radical scavenging and the relationship between structure and activity. Therefore, we have calculated the heat of formation and the geometry of both the parent compound and the corresponding radical using the ab initio program GAMESS. We have compared their differences in energy in order to gain insight into the stability of the radical and the ease with which it is formed. We have also investigated the spin density of the radical, to determine the delocalization possibilities. These calculated data were compared with experimental data from ESR (hyperfine coupling constants) and electrochemical oxidation (Ep/2) and were found to be in good agreement. By comparing the geometries of several flavonoids, we were able to explain the structural dependency of the antioxidant action of these compounds. The extremely good antioxidant activity of the flavonols could be explained by the formation of an intramolecular hydrogen bond.

Characterization of an Antioxidant-Enriched Beverage from Grape Musts and Extracts of Winery and Grapevine By-Products

“…This may explain the relatively high antioxidant activity of quercetin among flavonols, while the glycosylation of hydroxyl substituents on C3 will drop the antioxidant activity when compared to the aglycon [51]. Conjugated double bounds in combination with a planar molecular structure of quercetin allow for electron delocalization across the molecule, thus stabilizing the corresponding phenoxyl radicals [52]. In our study, both catechin dimers and quercetin derivatives increased in grapevine extracts, being the main ingredients of enriched grape juice.…”

Electrochemical Oxidation of Rutin

“…A two-step electron transfer reaction occurs at all pH values, associated with the loss of two protons. At high pH only one proton is lost resulting in a lower current [14]. The strong adsorption of rutin s oxidation products was confirmed since the oxidation peaks decreased drastically in the second scan for all pHs, Figure 5.…”

Flavones Inhibit LPS-Induced Atrogin-1/MAFbx Expression in Mouse C2C12 Skeletal Myotubes

“…The three classical antioxidant structural features of flavonoids are the presence of a B ring catechol group, the presence of a C2-C3 double bond in conjugation with an oxo group at C4 and the presence of both 3-OH and 5-OH (32)(33)(34). On the basis of this finding, the most effective antioxidant flavonoids in the nine flavonoids are assumed to be epicatechin, luteolin, keampferol, and delphinidin; however, these candidates with the inhibitory effect on atrogin-1 expression were not matched up to the two flavones selected in the present study (Fig.…”